High strength, heat resistant aluminum alloys

ABSTRACT

The present invention provides high-strength and heat resistant aluminum alloys having a composition represented by the general formula Al a  M b  La c  (wherein M is at least one metal element selected from the group consisting of Fe, Co, Ni, Cu, Mn and Mo; and a, b and c are atomic percentages falling within the following ranges: 
     
         65≦a≦93, 4≦b≦25 and 3≦c≦15), 
    
     the aluminum alloys containing at least 50% by volume of amorphous phase. The aluminum alloys are especially useful as high strength and high heat resistant materials in various applications and, since the aluminum alloys specified above exhibit a superplasticity in the vicinity of their crystallization temperature, they can be readily worked into bulk forms by extrusion, press working or hot forging in the vicinity of the crystallization temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to aluminum alloys having a desiredcombination of properties of high hardness, high strength, highwear-resistance and superior heat-resistance.

2. Description of the Prior Art

As conventional aluminum alloys, there have been known various types ofaluminum-based alloys such as Al-Cu, Al-Si, Al-Mg, Al-Cu-Si, Al-Zn-Mgalloys, etc. These aluminum alloys have been extensively used in avariety of applications, such as structural materials for aircrafts,cars, ships or the like; structural materials used in external portionsof buildings, sash, roof, etc.; marine apparatus materials, nuclearreactor materials, etc., according to their properties.

In general, the aluminum alloys heretofore known have a low hardness anda low heat resistance. In recent years, attempts have been made toachieve a fine structure by rapidly solidifying aluminum alloys andthereby improve the mechanical properties, such as strength, andchemical properties, such as corrosion resistance, of tee resultingaluminum alloys. But none of the rapid solidified aluminum alloys knownheretofore has been satisfactory in the properties, especially withregard to strength and heat resistance.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide novel aluminum alloys which have a good combination ofproperties of high hardness, high strength and outstanding corrosionresistance and which can be successfully subjected to operations, suchas extrusion, press working or a high degree of bending, at relativelylow cost.

According to the present invention, there are provided high-strength,heat resistant aluminum alloys having a composition represented by thegeneral formula:

    Al.sub.a M.sub.b La.sub.c

wherein:

M is at least one metal element selected from the group consisting ofFe, Co, Ni, Cu, Mn and Mo; and

a, b and c are atomic percentages falling within the following ranges:

    65≦a≦93, 4≦b≦25 and 3≦c≦15,

the aluminum alloys containing at least 50% by volume of amorphousphase.

The aluminum alloys of the present invention are very useful ashigh-hardness material, high-strength material, highelectrical-resistant material, wear-resistant material and brazingmaterial. Further, since the aluminum alloys exhibit a superplasticityphenomenon at temperatures near the crystallization temperaturesthereof, they can be subjected to extrusion, pressing and otherprocessings. The aluminum alloys such processed have good utility ashigh strength and high heat-resistant materials in a variety ofapplications because of the high hardness and high tensile strength.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a schematic view of a single roller-meltingapparatus employed to prepare ribbons from the alloys of the presentinvention by a rapid solidification process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aluminum alloys of the present invention can be obtained by rapidlysolidifying melt of the alloy having the composition as specified aboveby means of a liquid quenching process. The liquid quenching techniqueis a method for rapidly cooling molten alloy and, particularly, singleroller melt-spinning technique, twin roller melt-spinning technique andin- rotating-water melt-spinning technique, etc. are mentioned aseffective examples of such a technique. In these processes, the coolingrate of about 10⁴ to 10⁶ K/sec can be achieved. In order to produceribbon materials by the single roller melt-spinning technique or twinroller melt-spinning technique, molten alloy is ejected through a nozzleto a roll of, for example, copper or steel, with a diameter of about30-3000 mm, which is rotating at a constant rate of about 300-10000 rpm.In these techniques, various ribbon materials with a width of about1-300 mm and a thickness of about 5-500 μm can be readily obtained.Alternatively, in order to produce wire materials by thein-rotating-water melt-spinning technique, a molten jet of molten alloyis directed under application of the back pressure of argon gas, througha nozzle into a liquid refrigerant layer with a depth of about 1 to 10cm which is formed by centrifugal force in a drum rotating at a rate ofabout 50 to 500 rpm. In such a manner, wire-like materials can bereadily obtained. In this technique, the angle between the molten alloyejecting from the nozzle and the liquid refrigerant surface ispreferably in the range of about 60° to 90° and the ratio of thevelocity of the ejected molten alloy to the velocity of the liquidrefrigerant surface is preferably in the range of about 0.7 to 0.9.

Besides the above process, the alloy of the present invention can bealso obtained in the form of thin film by a sputtering process. Further,rapidly solidified powder of the alloy composition of the presentinvention can be obtained by various atomizing processes, for example,high pressure gas atomizing process or spray process.

Whether the rapidly solidified alloys thus obtained above are amorphousor not can be known by checking the presence of the characteristic halopatterns of an amorphous structure using an ordinary X-ray diffractionmethod. The amorphous structure is transformed into a crystallinestructure by heating to a certain temperature (i.e., crystallizationtemperature) or higher temperatures.

In the aluminum alloys of the present invention specified by the abovegeneral formula, a is limited to the range of 65 to 93 atomic % and b islimited to the range of 4 to 25 atomic %. The reason for suchlimitations is that when a and b stray from the respective ranges, theintended alloys having at least 50 volume % of amorphous region can notbe obtained by the industrial cooling techniques using theabove-mentioned liquid quenching, etc. The element M is selected fromthe group consisting of Fe, Co, Ni, Cu, Mn and Mo and has an effect inimproving the capability to form an amorphous structure. Further, theelement M, in combination of La, not only provide significantimprovements in the hardness and strength but also considerablyincreases the crystallization temperature, thereby resulting in asignificantly improved heat resistance.

The reason why c is limited to the range of 3 to 15 atomic % is thatwhen La is added in this range, considerably improved hardness and heatresistance can be achieved. When c is beyond 15 atomic %, it isimpossible to obtain the alloys having at least 50 volume % of amorphousphase.

Further, since the aluminum alloys of the present invention exhibitsuperplasticity in the vicinity of their crystallization temperatures(crystallization temperatures±100° C.), they can be readily subjected toextrusion, press working, hot forging, etc. Therefore, the aluminumalloys of the present invention obtained in the form of ribbon, wire,sheet or powder can be successfully processed into bulk by extrusion,pressing, hot forging, etc., at the temperature range of theircrystallization temperatures±100° C. Further, since the aluminum alloysof the present invention have a high degree of toughness, some of themcan be bent by 180° without fracture.

Now, the advantageous features of the aluminum alloys of the presentinvention will be described with reference to the following examples.

EXAMPLE 1

Molten alloy 3 having a predetermined alloy composition was prepared bhigh-frequency melting process and was charged into a quartz tube 1having a small opening 5 with a diameter of 0.5 mm at the tip thereof asshown in the FIGURE. After heating and melting the alloy 3, the quartztube 1 was disposed right above a copper roll 2, 20 cm in diameter.Then, the molten alloy 3 contained in the quartz tube 1 was ejected fromthe small opening 5 of the quartz tube 1 under the application of anargon gas pressure of 0.7 kg/cm² and brought into contact with thesurface of the roll 2 rapidly rotating at a rate of 5,000 rpm. Themolten alloy 3 is rapidly solidified and an alloy ribbon 4 was obtained.

According to the production conditions as described above, 20 differentkinds of alloys having the compositions given in Table were obtained ina ribbon form, 1 mm in width and 20 μm in thickness, and were subjectedto X-ray diffraction analysis. In all of the alloys, halo patternscharacteristics of amorphous metal were confirmed.

Further, crystaliization temperature (Tx) and the hardness (Hv) weremeasured for each test specimen of the alloy ribbons and there wereobtained the results as shown in Table. The hardness is indicated byvalues (DPN) measured using a Vickers microhardness tester under load of25 g. The crystallization temperature (T_(x)) is a starting temperature(K) of the first exothermic peak on the differential scanningcalorimetric curve which was conducted for each test specimen at aheating rate of 40 K/min. In the column of "Structure", characters "a"and "c" represent an amorphous structure and a crystalline structure,respectively.

                  TABLE                                                           ______________________________________                                             Composition                   TX    Hv                                        (by at. %)   Structure                                                                              Toughness                                                                             (K)   (DPN)                                ______________________________________                                         1.  Al.sub.75 Fe.sub.20 La.sub.5                                                               a        brittle 721   203                                   2.  Al.sub.75 Fe.sub.15 La.sub.10                                                              a        brittle 683   182                                   3.  Al.sub.80 Fe.sub.15 La.sub.5                                                               a + c    brittle 654   341                                   4.  Al.sub.80 Fe.sub.10 La.sub.10                                                              a        brittle 636   268                                   5.  Al.sub.85 Fe.sub.7.5 La.sub.7.5                                                            a        tough   626   256                                   6.  Al.sub.70 Co.sub.20 La.sub.10                                                              a + c    brittle 793   414                                   7.  Al.sub.72 Co.sub.18 La.sub.10                                                              a        brittle 721   531                                   8.  Al.sub.75 Co.sub.15 La.sub.10                                                              a        brittle 672   519                                   9.  Al.sub.85 Co.sub.7.5 La.sub.7.5                                                            a        tough   605   505                                  10.  Al.sub.75 Ni.sub.20 La.sub.5                                                               a        brittle 718   480                                  11.  Al.sub.80 Ni.sub.10 La.sub.10                                                              a        tough   628   465                                  12.  Al.sub.85 Ni.sub.7.5 La.sub.7.5                                                            a        tough   559   421                                  13.  Al.sub.88 Ni.sub.9 La.sub.3                                                                a        tough   439   393                                  14.  Al.sub.90 Ni.sub.5 La.sub.5                                                                a + c    tough   523   464                                  15.  Al.sub.85 Cu.sub.7.5 La.sub.7.5                                                            a        tough   497   442                                  16.  Al.sub.85 Mn.sub.7.5 La.sub.7.5                                                            a        tough   615   511                                  17.  Al.sub.85 Mo.sub.7.5 La.sub.7.5                                                            a        tough   511   493                                  18.  Al.sub.80 Cu.sub.5 Ni.sub.5 La.sub.10                                                      a        tough   535   472                                  19.  Al.sub.80 Ni.sub.5 Mo.sub.7.5 La.sub.7.5                                                   a        tough   570   450                                  20.  Al.sub.80 Fe.sub.5 Ni.sub.5 La.sub.10                                                      a        tough   585   380                                  ______________________________________                                    

As shown in Table, the aluminum alloys of the present invention have avery high hardness of about 200 to 530 DPN in comparison with thehardness of the order of 50 to 100 DPN of known aluminum alloys.Further, it is noteworthy that the aluminum alloys of the presentinvention have a high crystallization temperature of the order of about440° K. or higher, thereby resulting in a high heat-resistance.

What is claimed is:
 1. A high-strength, heat resistant aluminum alloyconsisting essentially of a composition represented by the generalformula:

    Al.sub.a M.sub.b La.sub.c

wherein: M is at least one metal element selected from the groupconsisting of Fe, Co, Ni, Cu, Mn and Mo; and a, b and c are atomicpercentages falling within the following ranges:

    65≦a≦93, 4≦b≦25 and 3≦c≦15,

said aluminum alloy containing at least 50% by volume of amorphousphase.